A Statistical Study about Transequatorial loops

1. A Statistical Study about Transequatorial loops Jie Chen National Astronomical Observatories Chinese Academy of Sciences

2. Transequatorial Loops(TELs) have relation to some solar physics phenomena • They may be relevant to solar dynamo model (Babcock,1961) • The evolution of TELs reflects magnetic reconnection (Tsuneta, 1996) • The disappearance or brighten of TELs has relation to CME or flare eruption (Khan et al.2000; Glover et al.) • Active regions which have the same chirality are more easily to form TELs (Canfield et al.1996; Farnik et al.1999; Pevtsov 2000)

3. Our Work Data Base and Observation • Whole YOHKOH/SXT data set (1991 October--2001 December) • SOHO/MDI and Kitt Peak full disk longitude magnetograms • We choose the images which are most clear and close to the middle of solar disk • Find 356 TELs

4. Category • According to the magnetic polarities that TELs connect the regions in photosphere: PTEL, FTEL PTEL SPTEL FTEL SFTEL

5. According to the numbers of TELs that the same region connected and magnetic polarities, we can classify TELs to SPTEL, SFTEL; DTELsA, DTELsB, DTELsC DTELsA DTELsB DTELsC

6. Statistical Results

7. Discussion • About bipolar group, the leading polarity is more compact and lives longer than the following polarity, the preceding polarity is more easy to form TELs than the following polarity, so PTEL has a larger proportion than FTEL • When the two active regions both are mature, then the following polarity has the same probability with the leading polarity, so DTELsA has a larger ratio

8. Preference Independent of Solar Cycle During solar cycle 22, in the northern hemisphere, the leading polarity is negative; during solar cycle 23, magnetic polarity is reversed

9. TELs number has the same trend with solar cycle The ratio of TELs to sunspot number is about 10% A: TELs number in different years B: the percent is TELs to sunspot number C: PTEL number in different years D: FTEL number in different years

10. Some Parameters about TELs • Separation: the footpoints distance between regions that TELs connected (Chase et al.,1977; Farnik et al.1999; Pevtsov, 2000 &2004) • Tilt Angle: the angle between TELs and equator (Pevtsov 2004) • Asymmetry in Latitude: the footpoints asymmetry in latitude of TELs These parameters reflect the properties of TELs and maybe have relation with solar dynamo Through compute flux-weighted center of the magnetic polarities, we calculate these parameters

11. Separation Mean value is about 270 (similar to Pevtsov(2000) result) It decreases from the minimum of solar cycle to maximum, this result is consistent to radial magnetic field variation following solar cycle

12. Tilt angle When the north footpoint is to the west of south footpoint, the angle is less than 900; reverse, it is more than 900 Mean value is about 900 Tilt angle value in different years

13. Asymmetry in Latitude If the latitude value in northern hemisphere is larger than it is in southern hemisphere, the result is more than 0; reverse, it is less than 0 Mean value is 0.6 Asymmetry in latitude is different in different years

14. Three Parameters are All Different in Different Solar Cycle

15. Result 1.About TELs, PTEL has a preference and this result is independent of solar cycle 2.TELs number variation following solar cycle and the ratio of TELs to sunspot number is about 10% 3. Separation, Tilt Angle, Asymmetry in Latitude is different in different solar cycle

16. Thank you!